Block duplicate emails sent from Salesforce

Maybe your SF support can help you figure out how to build a workflow that doesn't trigger for the same email if it has fired recently...

Forgive me, because it is possible this is what you are discussing in your problem #2: My organizations solution was Target Audience from Qualtrics. This will allow you to set up organizational setting so that a participant can not receive a survey every few days (1 day, 30 days, 90 days, whatever you set it at).

If that is what you discussed with Problem 2, please be aware of survey fatigue. Even if multiple cases close for one person in one day, you probably shouldn't be surveying them with every interaction (assuming of course this is some sort of satisfaction survey). Particularly if this is some sort of service-based-transnational survey; individuals will start dropping out of your panel like crazy.

We run 6 Transnational Surveys based off SF event triggers. Since I instituted a 90-day window within which our customers can not receive more than 1 survey invitation, not only have our completion rates tripled, our service scores ended up higher! When they aren't bothered to take too many surveys, they scored us higher because, in part, too many surveys were destroying their customer experience.